Hippocrates, a notable ancient Greek Physician, was really one of the first to get it right. He is often called the father of Neuroscience as a result. The man was able to uncover all of his concepts over 2,500 years ago without much to go on other than testing. Of course, it was minor testing at that. Unlike others of his time, Hippocrates believed that the human brain was not a cooling system.
Rather, he felt it was the seat of all thought, sensation, emotion, and cognition. This was slowly adopted into basic thought in the medical community. This is a pretty big deal because he was able to uncover something with only a bit of expertise in the area. Keep in mind, this was before major autopsies had been done. Therefore, Hippocrates had to go off of what he noticed and could hypothesize.